Living in an intelligent home
“Home automation” (aka “home control”) is the use of intelligent devices that are interconnected to one another enabling remote control and monitoring of said devices. Such systems include but are not limited to: lighting, heating, entertainment, and safety. In establishments such as apartments, homes, or corporate buildings, plenty of leeway exists for possible improvements in both comfort and safety. Energy resources such as gas, oil, and electricity can find feasible means of better efficiency. Driven by spiraling energy costs, demographic changes, and the increasing need for support and convenience in today’s home environment, home automation has made its way amongst today’s growing markets. With this breakthrough, planners, engineers, in addition to downstream users must maintain an overview on the wide array of providers and solutions available in the market as there are various forms of home networking used to create an automated or “intelligent” home.
Fig. 1: Many electrical functions in the home are are subject for central control logic.
The quest for an international standard
A fact that is frequently ignored is that communication networks only function if all the equipment in the network complies with the predefined rules or standards. There are two different approaches to this issue: Either all the equipment comes from a single manufacturer who ensures that their products are interoperable- otherwise known as the “closed standard”, or all the equipment manufacturers are obliged to comply with these special rules- otherwise known as the “open standard”. From a consumer’s perspective, the open standard is most advantageous because the market usually provides a greater selection of products at better prices. Looking at a company perspective, an open standard is indeed beneficial because it encourages market growth. Companies themselves can also exploit synergies by focusing on the products in which they specialize- while understanding that others supply complimentary and interoperable products.
The lack of an affordable, internationally recognized standard for home equipment communication has been one of the major problems for the home control sector. In Germany, the wired system KNX standard (formerly installation bus) has established itself. It certainly works very well and very reliably, but it is also very expensive. Moreover, as this standard is a wired solution, KNX can only be effectively implemented in new build properties because precise planning is required in order to be able to arrange all the necessary lines and cables in the walls of a building during the construction period. Therefore, this solution is rarely used for renovations or leased apartments. On the flip side, there are a range of closed standard wireless connection protocols; however, the decision is in favor of the traditional electrical installation method because it is less costly. In order to promote the large market for modernization and conversion, there is a need for affordable wireless-based products in which both professional installation engineers and informed end-users can install with ease and without major expense.
Open to everything
Accordingly, a general and internationally recognized open standard is needed for wireless communication. This is where the previously described conceptual approaches- closed versus open- conflict again. As mentioned before, the open standard has crucial benefits. Using open Z-Wave technology as a concrete example, we can show how a stable network can be produced under the conditions of an 868 MHz frequency band.
Z-Wave was developed by the Danish company Zensys, which was then acquired in 2008 by the USA-based semiconductor manufacturer Sigma Designs. The goal was simple: define a sound protocol, open it to the public, and place it in the hands of an industry alliance for further development. The result: Z-Wave’s basic physical and media access control layers (PHY/MAC) have become a certified international standard by the International Telecommunications Union as ITU-T G.9959. The Z-Wave Alliance and its member companies maintain the upper layers of the communications standard, its development, application, and final product certification requirements. Sigma Designs and Mitsumi Corporation supply the communication modules with the complete protocol stack to various partners (OEMs), who then integrate the technology into their own products and launches these to the market.
Fig. 2: Z-Wave communications modules are implementations of the complete protocol stack.
Independent test laboratories certify product adherence to the standard ensuring interoperability. Only certified equipment can be sold as Z-Wave equipment.
Forward-thinking – backwards compatible
Being well aware of the opportunities in the home installation market- with correspondingly long investment cycles, the Z-Wave Alliance is committed to the principle of maintaining the backwards compatibility of existing equipment- in contrast to most other manufacturers in the sector. Anyone who buys a Z-Wave product today has the confidence that they are buying a product based on a long-lived stable standard. And even in ten years time, new products in the market will still work with those that a consumer has had for years. To enable this backward compatibility, Z-Wave has developed a meaningful and effective mechanism. In order to introduce new features into the existing standard with ease, each appliance must state what properties and options it has.
Colored LED lamps are one example of this. These were certainly not around when the Z-Wave standard was first released. Initially, LED lamps were treated as if they were normal incandescent lamps that were to be switched on, off, and also dimmed. The specification of a particular color was then added as a supplementary option. There is a demand for color LEDs to light up white if no color is specified. This is in order to make it possible to continue using an older “pre-color” dimmer controller, even if the light to be dimmed is capable of more functions. When newer controllers are used, they can also select the color in the case of colored LEDs, as well as dim and switch older monochrome lights naturally.
Stability creates confidence
Nonetheless, the result is a universally usable, powerful, and yet stable wireless protocol which allows equipment from different manufacturers to be operated side by side in an installation. The opportunity to integrate new equipment from new manufacturers into the existing network without complications leads to confidence among end customers as well as distributors. It is this stability and future-ready capability that attracts even some of the larger and better-known companies such as Honeywell, Danfoss, FAKRO, MERTEN and Verizon.
Frequency- unfriendly
Another challenge which Z-Wave has now successfully overcome is the problem with wireless frequencies: For home networking, only the unlicensed but usable 868 MHz and 2.4 GHz frequencies make sense. Because the 2.4 GHz band is already overpopulated by WLAN and Bluetooth, and these appliances transmit with high powers and occasionally very high bandwidth, all wireless protocols that can be taken seriously for home automation use the 868 MHz band- also referred to as the ISM (Industry Science Medicine) band. However, the use of the 868 MHz band is heavily regulated: firstly, the maximum transmission power is limited to 10 mW, secondly equipment must also transmit for a maximum of 1% of a time interval (duty cycle = 1%). Despite this, there are millions of appliances in this frequency band which interfere with each other. Therefore it is far from a trivial task when both the expansion and operation of a stable wireless network in a frequency band suffers from very heavy interference while also being limited on the time available. The data sent must be minimized while at the same time maintain stable wireless communication. Z-Wave uses a frequency modulation method for line coding and modulates signals on it with a birate of 40 kb/s.
Registration with acknowledgement of receipt
A very effective method for avoiding communication problems in wireless networks is meshing. Also, each appliance forwards messages from other appliances, which cannot themselves communicate directly with the desired communication partner. On the one hand, this increases a network’s wireless range substantially. On the other hand, alternative routings arise if the direct path to the recipient is blocked.
This intrinsically simple method conceals a number of challenges behind its practical implementation. In an IP network, in which the router forwards the data, these routes are matched dynamically to the networking options by appropriate protocols such as OSPF. This dynamic switching of communication routes is one of the reasons for the amazing robustness of the internet. The price for this dynamic routing, however, is a substantial communication overhead. This is unacceptable in a wireless network for home automation, especially in the regulated 868 MHz band.
This is why Z-Wave uses static source routing. This means that all conceivable routes in the network are stored in the transmitter. In other words, even before transmission, an actual route is selected and coded accordingly. Only if this call is unsuccessful are the alternative routes used.
Appliances which transmit using Z-Wave technology always try to first reach the receiver on the direct wireless path. If this fails, alternative routes over the networks are calculated from the data in order to set up a call over an alternative path. This guarantees that, only if all connection attempts fail, will a failed call be reported to the application and thus to the user. The transmitter is therefore using virtual registration with acknowledgement of receipt. In this way, buildings, especially existing structures, can be networked sensibly by means of wireless communication alone.
Summary
Meanwhile, the volume and quality of products fitted with Z-Wave has reached a level which makes professional installations feasible, even for demanding clients. The price also means that in-house service skills can also be sold in addition to the actual hardware. The necessary integration and networking knowledge is therefore available. The opportunities to extend freely programmable control components with proprietary solutions and scripts mean that there is sufficient scope for differentiation among one’s competitors. Clients want energy efficiency and convenience in their homes, but the complexity of the solutions obscures their understanding. The idea is simple: be open to everything.
About the author:
Christian Pätz is honorary professor for systems reliability at the Chemnitz Technical University and spokesperson of the Z-Wave Alliance in Europe.
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